Normal Physiology Small Bowel and Colon

Question 1

What is the mode of primary motility in the small bowel?

Answer 1

segmentation in the fed state –> peristaltic graident via pacemaker cells 9-12 contractions/min –> transit 3-5 hours

Question 2

What is the gastroileal reflex?

Answer 2

gastrin activates segmentation in ileum

Question 3

What is the intrinsic reflex arc?

Answer 3

mechanoreceptors activate motility in small bowel

Question 4

What is the migrating motor complex?

Answer 4

occurs during fasting state –> sequential organized short waves initiated by motilin in ileum –> accompanied by pyloric sphincter relaxation

Question 5

What initiates the migrating motor complex?

Answer 5

motilin in ileum

Question 6

What turns off the migrating motor complex?

Answer 6

gastrin secretion (meal time)

Question 7

Where is the vomiting center?

Answer 7

medulla: lateral reticular formation

Question 8

What are the vomiting afferents?

Answer 8

irritant receptors in gut and other organs

Question 9

What are the vomiting efferents?

Answer 9

vagal, phrenic, spinal, S, P/S

Question 10

Mechanism of vomiting

Answer 10

saliva –> upper intestine contraction –> pylorus contraction –> abdominal muscles/diaphragm contraction –> LES/esophagal dilation –> glottis closes

Question 11

Does the small bowel secrete enzymes?

Answer 11

no –> water and mucus for hydrolysis and lubrication (driven by Cl- secretion)

Question 12

What drives small bowel secretion?

Answer 12

Cl- secretion in crypts

Question 13

What regulates small bowel secretion?

Answer 13

cAMP

Question 14

What is the primary channel involved in small bowel secretion?

Answer 14

CFTR

Question 15

How is small bowel absorption regulated?

Answer 15

it is not –> absorbs everything isotonically and doesn’t concentrate the stuff unlike the kidney

Question 16

2 types of surface epithelial cells in small bowel

Answer 16

villus and crypt cells of lieberkuhn

Question 17

What is the function of villi?

Answer 17

absorption

Question 18

What is the function of crypts?

Answer 18

secretion of Cl-

Question 19

What is the average lifespan of intestinal epithelia?

Answer 19

3 days

Question 20

What enzyme initiates digestion of carbohydrates?

Answer 20

salivary amylase

Question 21

What carbohydrate digestion occurs in small bowel?

Answer 21

pancreatic amylase secretion and degradation of complex carbs to disaccharides –> final step = brush border disaccharidases

Question 22

How are sugars transported in the small bowel?

Answer 22

cotransport with Na+

Question 23

What enzyme initiates digestion of proteins?

Answer 23

HCl-pepsin in stomach

Question 24

What protein digestion occurs in small bowel?

Answer 24

pancreatic proenzymes activated in lumen –> enterokinase catalyzes trypsinogen –> protease activation –> final step = brush border aminopeptidases

Question 25

How are proteins transported in the small bowel?

Answer 25

1. cotransport with Na+ w/ carriers for neutral basic and acid AAs 2. cotransport of di/tripeptides with H+ and broken down into AAs in enterocyte

Question 26

What happens to fat in the lumen of the small bowel?

Answer 26

emulsification/digestion

Question 27

How is lipid absorbed by the small bowel?

Answer 27

micell transfer across apical cell membrane

Question 28

What happens to lipids in enterocytes?

Answer 28

processing and reconstitution into bigger lipid molecules for lymphatic/bloodstream export

Question 29

What lipodigestive mechanisms take place in the stomach?

Answer 29

1. gastric lipase breaks down TG --> FA and DG | 2. DG and phospholipids stabilize emulsion

Question 30

What lipodigestive mechanisms take place in the duodenum?

Answer 30

1. bile salts stabilize emulsion | 2. pancreatic lipase converts TG --> FA + MG

Question 31

What is inside a stable duodenal emulsion?

Answer 31

tg, dg, cholesterol, fat soluble vitamines

Question 32

What is outside a stable duodenal emulsion?

Answer 32

Phospholipids, MG, FA, bile salts --> hydrophilic

Question 33

What is colipase and where is it secreted?

Answer 33

pancreas --> brings lipase and TG together --> 50% decrease in lipase function without colipase

Question 34

What is phospholipase A2 and where is it secreted?

Answer 34

pancreas --> digests phospholipids on emulsion surface, helps anchor lipase to emulsion, activated by bile salts

Question 35

What activates phospholipase A2

Answer 35

bile salts

Question 36

Do brushborder enterocytes digest fat?

Answer 36

no

Question 37

What is the fate of bile salts?

Answer 37

some excreted but much of it eventually reabsorbed in terminal ileum

Question 38

How are fats packaged for transport to lymphatics?

Answer 38

chylomicrons coated with ApoA,B -->exocytic release

Question 39

How are vitamins digested?

Answer 39

they are not --> absorbed whole

Question 40

What are the fat soluble vitamins?

Answer 40

ADEK

Question 41

How is B12 absorbed?

Answer 41

IF from gastric parietal cells transport B12 from proximal bowel to ileum where IF-B12 complex is absorbed via transport protein at terminal ileum

Question 42

How are water soluble vitamins absorbed?

Answer 42

B, C via simple diffusion or carrier mediated transport

Question 43

Where does B12 bind intrinsic factor?

Answer 43

in proximal small bowel after bieng freed from carrier R protein

Question 44

Relative rate of absorption of salt/water in three parts of small bowel?

Answer 44

ileum > jejunum > duodenum

Question 45

How is salt/water absorbed in small bowel?

Answer 45

actively absorbed via Na+/K+ Atpase on basolateral membrane

Question 46

Is there more Na in the: lumen, cell, blood

Answer 46

blood

Question 47

Is there more K in the: lumen, cell, blood

Answer 47

cell

Question 48

What is the voltage of the lumen

Answer 48

-4mv

Question 49

What is the voltage of an enterocyte?

Answer 49

-60mv

Question 50

What is the voltage of blood next to an enterocyte?

Answer 50

0mv

Question 51

Functions of colon

Answer 51

salt and water absorption (no contentration), waste storage, no digestion

Question 52

| What is more permeable to ions? small/large bowel

Answer 52

| small bowel

Question 53

What ions are absorbed in colon?

Answer 53

Na/Cl/water

Question 54

What ions are secreted in colon?

Answer 54

K+ (unlike small bowel), HCO3

Question 55

What is more permeable to water? small/large bowel

Answer 55

colon is slower and absorbs less

Question 56

Small bowel or colon? digestion

Answer 56

SB

Question 57

Small bowel or colon? na/nutrient transport

Answer 57

SB

Question 58

Small bowel or colon? K secretion

Answer 58

colon

Question 59

Small bowel or colon? net hco3 secretion

Answer 59

large bowel

Question 60

Small bowel or colon? water absorption

Answer 60

sb > colon

Question 61

Small bowel or colon? concentration

Answer 61

neither

Question 62

What regulates segmentation?

Answer 62

ANS

Question 63

What is the gastrocolic reflex?

Answer 63

simultaneous strong contractions in proximal colon --> mass movement response to gastrin and extrinsic nerves

Question 64

What is secreted by bacteria that nourishes colon?

Answer 64

SCFA (short chain fatty acid), gas, vitamin K, stimulate immunity/IgA secretion

Question 65

T/F defecation involves both voluntary and involuntary muscles

Answer 65

T